The present invention relates to a battery system made up by connecting multiple battery modules, each thereof being made up by connecting multiple storage cells with each other, in parallel with multiple battery units, each thereof having a switching circuit connected in series to each of the battery modules.
An electric power system (a system in which power generation, power transformation, power transmission, and power distribution are integrated together) originating from natural energy, called renewable energy, such as wind power generation, solar power generation and so forth, has most recently been upgraded. The electric power system originating from the natural energy has an advantage in that a burden imposed on natural environments is less, but the generation capacity thereof is dependent on the natural environment on the other hand. More specifically, since the wind power and the intensity of sunlight vary from hour to hour, there is concern about a possibility that such variation will have an adverse effect on the electric power system such as frequency variation and voltage variation.
Progress has lately been made with certainty in development of a battery system for power storage, and experimental introduction thereof into the electric power system, as one of approaches for removing the concern.
In Japanese Unexamined Patent Application Publication No. 2011-211790, there is disclosed a battery system to be mounted in an electric vehicle, as a battery system according to the related art, the battery system being made up by connecting multiple battery modules, each thereof being made up by connecting multiple storage cells with each other, in parallel with multiple battery units, each thereof having a switching circuit connected in series to the battery module.
To describe the battery system in detail, the battery system according to Japanese Unexamined Patent Application Publication No. 2011-211790 includes multiple battery units connected in parallel with a power apparatus such as an inverter (for use in conversion of DC power into AC power), and so forth, a voltage sensor for detecting the respective voltage values of the plural battery units, and a controller for controlling respective outputs of the plural battery units. The switching circuit is made up by connecting a first circuit having a first switch connected in series to a precharge resistor, in parallel with a second circuit having a second switch. The first circuit, and second switches each are configured so as to open, or close according to a control signal of the controller.
With the battery system according to Japanese Unexamined Patent Application Publication No. 2011-211790, there are occasions when a battery unit is partially removed from the battery system in order to, for example, perform maintenance of individual battery units. There is possibility that the internal resistance of a storage battery with respect to the partially removed battery unit has varied from the internal resistance of a storage battery belonging to a battery unit connected to the battery system, owing to polarization, and so forth. If a battery unit is connected to the battery system without taking variation occurring to the internal resistance of the storage battery belonging to the battery unit connected to the battery system into consideration, there has existed the risk of an excess current flowing to the battery unit to serve as a target for connection.
In order to avoid such a problem as described, the controller first causes the first switch to be changed from the off condition over to the on condition at the time when the battery unit as the target for connection is connected to the battery system. By so doing, the battery unit is connected to the battery system via the pre-charge resistor. Thereafter, the controller causes the second switch to be changed over from the off condition to the on condition. By so doing, the battery unit is directly connected to the battery system not by the intermediary of the pre-charge resistor.
With the battery system according to Japanese Unexamined Patent Application Publication No. 2011-211790, upon the battery unit to serve as the target for connection being connected to the battery system, it is possible to deter an excess current such as a rush current and so forth, capable of flowing immediately after the connection.